1. Field of the Invention
The present invention relates to method and apparatus for carrying out heat treatment with respect to a substrate, and to a method of forming a photo resist film or chemically amplified resist film pattern on a substrate.
2. Description of the Related Art
In the process of manufacturing semiconductor devices, resist pattern is used to form element regions and to process electrode interconnects. The resist pattern is formed in the following manner in general. A resist coating film is formed on semiconductor wafer, and thereafter, heat treatment calling pre-bake is carried out. The pre-bake is carried out to volatilize solvent contained in the resist. Predetermined pattern is transferred to the resist film by exposure.
With micro-fabrication of semiconductor elements, high resolution is required in the lithography process. In order to meet the requirement, the wavelength of used exposure light is shortened. In photolithography, KrF excimer laser (wavelength: 248 nm) has been widely used as an exposure light source.
On the other hand, as the wavelength of exposure light is shortened, photo resist calling chemically amplified resist has been proposed and practically used as the photo resist material to which pattern is transferred. The chemically amplified resist contains acid generating agent generating acid by exposure. The acid generated by exposure decomposes resin (positive-tone resist), and cross-links it (negative-tone resist). This serves to make use of the property such that solubility to developer changes in the development process after that.
The chemically amplified resist has property excellent in resolution while it is very delicate with respect to environment. More specifically, the chemically amplified resist reacts with basic substances in atmosphere; for this reason, acid is inactivated. This is a factor of causing degradation in pattern shape and resolution. In order to prevent the degradation, environmental control is carried out. In general, the environmental control is carried out in a manner of providing chemical filters in an aligner (exposure system) and in a coater developer for making resist coating and developing processes.
Most of the chemically amplified resists require heat treatment process calling PEB (Post Exposure Bake) after exposure process. The PEB is carried out in order to diffuse acid generated in the exposure process. The PEB process is carried out, and thereafter, the chemically amplified resist is developed so that resist pattern can be formed.
In the PEB process, there has been known that acid is evaporated in addition to the foregoing acid inactivation. Some methods have been conventionally proposed as the method of preventing the acid evaporation of the chemically amplified resist in the PEB process. For example, one is the method of setting pre-bake temperature used for volatilizing solvent after resist coating higher than usual, and setting PEB temperature lower than usual, and thereby, reducing acid evaporation. (See Effect of acid evaporation in chemically amplified resists on insoluble layer formation, Journal of photopolymer science and technology Vol. 8, Number 4 (1995) p. 561–570). Another is the method of carrying out the PEB process under the pressure higher than usual, and thereby, reducing acid evaporation (See JPN. PAT. APPLN. KOKAI No. 11-38644).
The pre-bake temperature and the PEB temperature are changed, and thereby, the acid evaporation in the PEB process can be reduced. However, pre-bake and PEB processes are carried out under conditions largely diverging from the optimized temperature condition (normal condition). For this reason, it is difficult to sufficiently show performances such as exposure and focus margin the resists possess naturally.
In the PEB process, a heating apparatus, which can solve the following problem, is required. Namely, gas and fine grain generated in heating adhere into a chamber; therefore, this is a source of the generation of particle. For this reason, it is general that purge air stream is formed in the chamber of the heating section. However, acid evaporated in PEB is carried to the downstream side by the purge air stream, and adsorbs to the surface of resist film. Therefore, acid concentration on resist surface differs in chips situated on the most upperstream to the air stream and chips situated on the downstream side. As a result, non-uniformity occurs in resist dimension in the wafer surface after development.
If pressure is set higher in the PEB process, acid evaporation is reduced; however, suitable course is not taken to the problem that the adsorption of the evaporated acid. The evaporated acid adsorbs to semiconductor wafer: for this reason, it is difficult to prevent the occurrence of non-uniformity of resist dimension in the wafer surface after development.